In a transmission electron microscopy system, an electron beam is directed onto a sample, and electrons having traversed the sample are detected in an analyzing system disposed in the beam path downstream of the sample, in order to obtain information relating to properties of the sample. The electrons incident on the sample traverse the sample un-scattered or are scattered within the sample by a certain angle, and/or change the kinetic energy within the sample.
One possible way of analyzing the electrons having traversed the sample includes separating of electrons having traversed the sample substantially un-scattered from electrons scattered by a significant angle while traversing the sample. Electrons which are scattered in the sample by a significant angle are commonly referred to as dark field electrons, while electrons traversing the sample substantially un-scattered are commonly referred to as bright field electrons. An image, commonly referred to as a bright field image can be obtained from detected local intensities of bright field electrons, while an image commonly referred to as a dark field image can be obtained from detected local intensities of dark field electrons.
Dark field images are typically useful for visualizing sample structures provided by heavy elements, such as elements heavier than iron. On the other hand, bright field images are typically useful for visualizing sample structures formed of light elements, such as elements lighter than iron. However, sample structures provided by very light elements, such as elements lighter than carbon, are difficult to be visualized by bright field images since very light elements scatter electrons traversing the sample by only a very small amounts and impose only very small phase changes on electrons traversing the sample.
An analyzing method has been proposed which is referred to as “Annular Bright Field Imaging” (ABF) and in which a ring-shaped detector is used for detecting bright field electrons having traversed the sample along directions having an angle relative to the optical axis greater than a minimum angle which is different from zero.